This invention relates to mixing heads used in the environmental remediation industry for mixing and agitating waste or sludge. At most hazardous waste sites, contaminated soil, chemicals, and trash are held in a containment pond. This waste must be thoroughly mixed with reagents or cement to render it either harmless or less likely to migrate to water-bearing strata. Operators have used excavating machinery such as bucket loaders to do this mixing. However, specially adapted mixers are much more efficient. In the present state of the art, such mixers use augers, belts having cutting teeth, or horizontally-rotating mixing heads. Ideally, the operator of the mixing machinery should be able to move the mixing head over the area to be mixed while also controlling its depth and the speed of the mixing. This can be difficult to do with current mixing heads which rotate along an axis substantially horizontal to the surface of the earth. Because of their relatively large surface area to weight ratio, horizontal mixing heads are not easily forced deep into waste ponds, and they tend to become stuck under heavy overburden. Further, horizontally rotating mixing heads are easily tangled in the scrap and wire often found in waste sites. Other mixing machines use augers, but augers also become tangled in scrap and have poor mixing abilities. A mixing head must operate in a hostile environment. It is likely the wastes to be mixed will be dense, contain corrosive chemicals, large heavy objects which can break mixing arms, and also fine abrasive particles which can quickly wear out mixing arms and bearings. The prior-art horizontal mixing heads have unprotected shafts and seals which are particularly susceptible to this kind of wear. Prior-art mixing machines are further susceptible to rapid wear and failure because they do not incorporate the combination of protected thrust bearings and radial bearings of the present invention.
There is thus a need for a mixing head having sufficient power to mix heavy material, easily moveable both laterally and vertically, and resistant to tangling or impact with heavy objects. Such a mixing head should also resist the effects of corrosive and abrasive material in the mixing site. One embodiment of a mixing head having the desired characteristics is described in our U.S. patent application, filed Dec. 17, 1997, which is issued as U.S. Pat. No. 5,836,690, which application is incorporated by reference in to this present application.